It might see a few of the existing flat earthers harden their view, but I suspect they'll gain fewer followers overall when hidden from mainstream content. What's interesting is that fracturing hateful communities does decrease the spread of their message[0]. I have to think that we could see similar trends with fringe theories, like the earth being flat, or bleach being a cure for autism. Which would in turn prevent users who might fall into the rabbit-hole that is the cesspool like communities among hate based groups, and the more fringe theories (again, flat earthers, anti-vax luancy, etc.)
This is basically what happened when Reddit banned racist subreddits. Everyone cried
"But my free speech!"
"Won't they just polarize even harder?"
"Won't they just operate in the ShAdOwS?"
Except that didn't happen. The people left for Voat, and then Voat died. Banning harmful communities works time-and-time again, and it would work for YouTube if they actually did anything. For every 'guideline update' or press release they do about content moderation, they do basically nothing. The one exception was the sketchy videos with children, but their solution has been pretty heavy-handed and reactionary. I think that's the problem: YouTube has never been pro-active in moderating its platform and it shows.
Even more interesting on that article I linked about exactly that: the people who stayed stopped being as racist / hateful towards fat people. They didn't drag their garbage ideas along to the new places they started posting (on reddit). It wouldn't surprise me if some of them even evolved a little and abandoned those views.
I'm proof-reading a book that a friend of mine is writing about how normal right-wing/conservative populism becomes corrupted by fascist/hate stuff, and a big part of it is hate groups actively "normalizing" their content and spreading it via mainstream social media like twitter and youtube. That way, they show up alongside more mainstream political thought. If hate speech, even "polite" hate speech, is consigned to its own dedicated world rather than sharing ours, it doesn't spread the same way.
0: https://medium.com/acm-cscw/you-cant-stay-here-the-efficacy-...